When the Kidneys Fail
The urinary system can be damaged by disease, infection or lifestyle. In kidney (renal) failure, the kidneys can no longer filter the blood properly, so wastes such as urea and excess water and salts build up. This upsets homeostasis and can be life-threatening. Common causes include long-term high blood pressure, uncontrolled diabetes, and severe infections.
Common Problems
- Kidney stones: hard lumps formed from minerals (such as calcium salts) in concentrated urine. They can block the ureter and cause severe pain. Drinking enough water lowers the risk.
- Urinary tract infection (UTI): bacteria infect the bladder or urethra, causing pain and frequent urination.
- Kidney failure: loss of filtering function, shown by high blood urea and reduced urine output.
Remember
Drinking plenty of water, controlling blood pressure and blood sugar, and not overusing painkillers all help protect the kidneys.
Treatments for Kidney Failure
Two main treatments restore the balance that failed kidneys cannot maintain:
- Dialysis: a machine (haemodialysis) filters the patient's blood across a partially permeable membrane. Wastes and excess salts diffuse out of the blood into dialysis fluid, while useful substances at the right concentration stay in. It must be repeated several times a week.
- Kidney transplant: a healthy kidney from a matched donor replaces the function of the failed kidneys. It is a longer-term solution, but the patient must take drugs to prevent rejection.
Example
In dialysis, the dialysis fluid has the same glucose concentration as normal blood, so no net glucose is lost, while it contains no urea, so urea diffuses out of the blood down its concentration gradient.